Fair value measurements - Gains (Losses) Due to Changes in Fair Value for Financial Instruments Measured at Fair Value Using Fair Value Option (Detail) - JPY (¥) ¥ in Billions		12 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Short-term borrowings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[2]	¥ 14	¥ 11	¥ 0
Collateralized financing [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[3]	6	(2)	(3)
Long-term borrowings [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[2],[4]	79	(7)	11
Other liabilities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[5]	(2)	0	0
Total
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1]	97	2	8
Trading assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[6]	1	0	0
Private equity investments [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[6]	1	1	0
Loans and receivables [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1]	5	4	3
Collateralized agreements [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[3]	2	4	4
Other assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1],[6]	(22)	6	17
Total
Fair Value, Option, Quantitative Disclosures [Line Items]
Gains/(Losses)	[1]	¥ (13)	¥ 15	¥ 24

[1] Includes gains and losses reported primarily within Net gain on trading, Gain on private equity investments and Revenue-Other in the consolidated statements of income.

[2] Includes structured notes and other financial liabilities.

[3] Includes reverse repurchase and repurchase agreements.

[4] Includes secured financing transactions arising from transfers of financial assets which did not meet the criteria for sales accounting.

[5] Includes unfunded written loan commitments.

[6] Includes equity investments that would have been accounted for under the equity method had Nomura not chosen to elect the fair value option.